1. Field of the invention
This invention relates to an improved composition for use in absorption refrigeration systems or heat pumps.
2. Description of the Prior Art
In general, the absorption refrigeration system is a closed circuit containing a refrigerant-absorption liquid composition or solution therein. The refrigeration is effected by evaporating the liquefied refrigerant in an evaporator of the circuit. The refrigerant vaporized in the evaporator is then brought into contact with and absorbed in a weak solution or a solution with a low concentration of the refrigerant in an absorber. The resulting strong solution, i.e. a solution having a high concentration of the refrigerant, is applied with heat from an external heat source to release the refrigerant vapor. The vaporized refrigerant is then condensed in a condenser whereupon heat generates, and again fed into the evaporator as the liquefied refrigerant. On the other hand, the solution from which the refrigerant vapor has been released is fed back into the absorber as the weak solution, in which the refrigerant vapor is again absorbed.
The highest possible effect of this cooling and heating mode of operation can be attained only when the strong solution is held at high temperatures in the generator.
In order to realize the maximum effect, there has been proposed a refrigerant-absorption liquid composition which comprises monochlorodifluoromethane (R-22) as a refrigerant and N, N-dimethylformamide (DMF) as an absorbent. However, either absorption refrigeration machines or heat pumps using this composition have never been put into practice yet. One of reasons for this is considered due to the fact that when the above composition is heated to high temperatures over about 120.degree. C., R22 decomposes into products such as hydrochloric acid and hydrofluoric acid with the attendant decomposition of DMF, so that not only the apparatus is damaged by corrosion, but also there arises the vital problem that R22 and DMF deteriorate in their physical and chemical properties.
Another type of absorption liquid-refrigerant composition, which comprises tetraethylene glycol dimethyl ether (TEGDME) as an absorbent, has also been proposed as being more chemically stable than the above-described composition. Although this composition has improved heat stability over the first-mentioned composition only by 20.degree.-40.degree. C., its life is insufficient for practical applications. For instance, when a composition composed of R-22 and TEGDME is heated to over 150.degree. C., these two components considerably deteriorate in physical and chemical properties similar to the R-22/DMF composition.
It is well known in the art that R-22 is relatively stable among various fluorinated hydrocarbons, DMF yields decomposition products such as an amine when coexisting with metals, and TEGDME is one of the most stable materials as an organic solvent. Nevertheless, when applied, in combination, as a composition for absorption refrigeration, these compounds undergo much more rapid and complicated deterioration and decomposition reactions than expected from the thermal stabilities of the individual compounds. These deterioration and decomposition reactions take place in very different and complicated manners according to the constituent components and combinations thereof, and hence it is very difficult to thermally stabilize those compositions at high temperatures. This is why the refrigerant-absorption liquid compositions using combinations of R22 and DMF and R22 and TEGDME have not been reduced into practice yet in spite of their better physical and chemical properties than those of other known compositions.